It took nearly seven years, but the tussle between OK! and Hello! over unauthorised photographs of the wedding of Catherine Zeta-Jones and Michael Douglas finally drew to a close last week. When it was launched, the case represented the first test of whether the then newly enacted human rights legislation would lead to a new law of privacy in Britain. Now that it has concluded, clear outlines of that privacy law are emerging.

Traditionally English law did not recognise a right of privacy. Sixteen years ago when the 'Allo 'Allo actor Gorden Kaye brought an action over an intrusive and unauthorised "interview" conducted with him in a hospital bedroom, the courts said firmly that there was no law of privacy in the UK.

But in 2000 the Human Rights Act came into force, enshrining in law a citizen's right to respect for a "private and family life". The courts were quick to use this new right to grant effective privacy protection in a number of cases. And over the past six months, court decisions have taken in many important privacy issues, from private journals to adultery, from surreptitious photographs to "kiss and tell".

Last week's conclusion of the celebrity magazine battle, coupled with the attempts by the BP chief executive Lord Browne to prevent former lover Jeff Chevalier telling all to the Mail on Sunday, show how far privacy law has developed in the intervening period.

Things really began to change in 2000 when an unauthorised photographer infiltrated the Douglas/Zeta-Jones wedding. His surreptitious snaps were transmitted to Hello!, enabling it to spoil OK!'s expensive exclusive on the same event. The courts accepted that the privacy of the Douglases had been infringed by the unauthorised pictures, and the couple were awarded modest damages for distress.

But in the end, the real issue in the Douglas case was about the buying and selling of "privacy rights". Having sold the right to publish wedding photographs to one celebrity magazine, were the couple and OK! entitled to prevent Hello! from publishing photographs of the same event? The court of appeal decided that OK! had no claim for the revenue lost as a result of the Hello! "spoiler", but last week the House of Lords reversed this, saying that Hello! owed a direct obligation in confidence to OK! and allowed the loss - valued at £1m - to be recovered. The act of being a celebrity or running a celebrity magazine was held to be a "lawful trade", and traders in such commodities are entitled to protection over the commercial value of their business.

The Lord Browne case involved more intimate matters. Most of the media attention focused on the lie which Lord Browne told the court and which led to his downfall. But this made little difference to the result. The courts engaged in careful analysis of the extent to which a person can expect conversations with friends and lovers to remain confidential, and decided Lord Browne was entitled to the protection of privacy for the private expression of views about his colleagues and communications about business matters to a sexual partner.

An injunction was, however, refused in relation to some items of information concerning BP which shareholders and colleagues had a proper interest in knowing. The court was not concerned about the truth or falsity of the allegations by Chevalier but whether there was a proper interest in disclosing them.

The court of appeal permitted the publication of only the "bare fact" of the past relationship between Lord Browne and Chevalier on the basis that, without mention of it, the publication of the "public interest" material would not make sense.

Both these cases show how far privacy law has moved since the Gorden Kaye case. The basic outline of this law can now be summarised in five points:

1. The law will protect information which is "obviously private" or where there is a reasonable expectation of privacy.

The question is deceptively simple: was there a reasonable expectation that the information will remain private? The approach is flexible. The court looks at the nature of the information, the form in which it is conveyed as well as the relationship between the person disclosing and the person making the claim. Sometimes information is obviously private, such as the contents of Prince Charles' private travel journals. Information about sexual or financial matters will also obviously be protected as would be the kind of "revelations" in most tabloid "kiss and tell" stories.

2. The law will protect potentially private information even if it is false.

Many newspaper stories about private life are a heady mixture of the true and the made up. It has often been argued that no privacy can lie in false information. However, it was established in a case brought by Canadian folk singer Loreena McKennitt that "the truth or falsity of the information is an irrelevant inquiry in deciding whether the information is entitled to be protected". A made up story about a person's intimate life is just as objectionable as a true one.

3. The availability of information to others is no longer decisive.

The fact that the information has previously been made known to others does not always mean that it is no longer private. The fact that information is known to friends or work colleagues does not mean that a newspaper is free to publish to the whole world. Even prior publication in the media is only one factor in considering whether information merits future protection. Particularly in the case of photographs, the court may prevent a republication of something which has already been widely distributed. Most starkly in the Douglas case, even though OK! had published pictures of the wedding, it still enjoyed confidentiality in other pictures of the wedding even though it would be hard to identify any real additional information in these further pictures not already published.

4. Publication of private information can be justified in the public interest.

The public interest is not the same as what the public is interested in. There is no real public interest in the publication of "vapid tittle-tattle about the activities of footballers' wives and girlfriends". The court looks at the balance between the right to privacy (under article 8 of the European Convention on Human Rights) and the right to freedom of expression (under article 10). Neither takes priority. The nature of the private information and the "type of expression" are taken into account - publications which contribute to a "debate of general interest" are likely to be permitted. Those which contribute only to public entertainment are likely to be restrained.

5. Everything depends on context, circumstances and impression.

Privacy cases are decided not on the basis of strict rules but on the facts. In this, different judges can take radically different views in relation to the same set of facts. It is striking that in both the Douglas case and the celebrated privacy case brought by Naomi Campbell, of the nine judges which heard each case as it went from trial, through the court of appeal to the House of Lords, five opposed the privacy complaint and four supported it. In each case three of the four were in the House of Lords, so the claims succeeded. So while the legal principles are becoming clearer, a consensus among the judiciary as to what is and what is not an invasion of privacy in any particular case remains elusive.

These five points provide a rough guide to the new territory of privacy. Under the influence of human rights case law from Strasbourg we are moving slowly but inescapably towards the stricter privacy protection of French or Italian law. With each decision, the new law is becoming clearer and more robust. The law of privacy has finally come of age.

· Hugh Tomlinson QC is a barrister at Matrix chambers. Dan Tench is a media partner at Olswang solicitors